1. Field of the Invention
This invention pertains to cable handling, and more particularly to apparatus for laying underground cable.
2. Description of the Prior Art
The contribution of fiber-optics to the communications age is well known. With fiber-optics, thousands of messages can be transmitted simultaneously through a single fiber.
A major problem associated with fiber-optic technology concerns the placement and protection of the fiber-optic cables. It is generally accepted practice to lay fiber-optic cables underground below the frost line. Various equipment has been developed to efficiently lay the cable across fields and other unobstructed areas. However, substantial difficulties are encountered when the fiber-optic cable must be laid under such obstructions as highways, railroads, and gas and oil pipelines. Splicing fiber-optic cables is both costly and detrimental to the strength and quality of the light signals to be pulsed through the cables.
To lay splice-free cables under various obstructions, it is known to unwind an entire supply reel of cable at the obstruction. The cable is pulled back and strung in one or more long loops stretching away from the obstruction. The cable free end is then fed through a bore under the obstruction. Finally, the cable is rewound on the supply reel located on the downstream side of the obstruction. A variation of the pull-back method is the FIG. 8 method. The cable is entirely unwound from the supply reel, but it is laid in the form of several overlapping figure-8s on the ground. Both the pull-back and figure-8 methods are very time consuming and therefore costly ways of passing cables under obstructions. Further, laying the fiber-optic cables on the ground renders them susceptible to damage by machinery and personnel in the area.
Manitou Industries of Neilburg, Saskatchewan, Canada has developed apparatus that eliminates the need for laying the cable on the ground at an obstruction. The Manitou device employs a pair of special cable reels that give access to the cable free end underlying the overlying cable of the supply reel. At an obstruction, the plow supply reel is unloaded from the plow and placed on the ground. The cable free end is pulled from the special reel and is partially unwound by an unwinding tower attached to the reel. The cable free end is passed under the obstruction. The cable free end is then wound onto a second special reel on a trailer located on the downstream side of the obstruction simultaneously with unwinding the cable from the original supply reel attached to the unwinding tower. The second reel is then unloaded from the trailer and loaded onto the plow, where it becomes the plow supply reel for supplying cable until the next obstruction is reached. At the next obstruction, the reel unloading, unwinding, rewinding, and reloading process is repeated. Although the Manitou system is an improvement over merely laying the cable on the ground, it nevertheless requires substantial time to unload and load two reels at the obstructions. Further, a substantial expenditure is required for the special reels and the machinery for handling them.
Thus, a need exists for improved apparatus and methods for laying continuous underground cables.